Conventionally, various ultrasonic wave transceiving devices for displaying a sea bottom as well as a school-of-fish at the same time, and also additional information of the school-of-fish or the water bottom have been devised. For example, JP1999-052048A discloses an underwater detecting device that transmits one kind of ultrasonic signals, and displays a detection image as well as discriminating a water bottom sediment type by using echo signals obtained from the transmitted ultrasonic signals.
However, ultrasonic signals have different reflection characteristics between a school-of-fish and a water bottom sediment. Therefore, in a case where the configuration and the method of JP1999-052048A are used and the ultrasonic signal is adjusted to accurately discriminate, for example, the school-of-fish, then the water bottom sediment type cannot be discriminated accurately. Conversely, in a case where the ultrasonic signal is adjusted to accurately discriminate the water bottom sediment type, then the school-of-fish cannot be discriminated accurately.
Therefore, other various ultrasonic wave transceiving devices for transmitting different ultrasonic signals for school-of-fish detection (for an echo image) and water bottom sediment type discrimination (for additional information) have been devised. Further, there also exist ultrasonic wave transceiving devices for transmitting ultrasonic signals for school-of-fish detection at two different frequencies and transmitting ultrasonic signals for water bottom sediment type discrimination at two different frequencies in order to improve the function for the school-of-fish detection as well as the function for the water bottom sediment type discrimination.
FIG. 10 is a view showing a conventional transception concept. The conventional ultrasonic wave transceiving device transmits first ultrasonic signal FM(H)Tx and second ultrasonic signal FM(L)Tx for school-of-fish detection sequentially in series. The first and second ultrasonic signals FM(H)Tx and FM(L)Tx have the same pulse length therebetween. The frequency of the signal forming the pulse of the first ultrasonic signal FM(H)Tx is higher than that of the second ultrasonic signal FM(L)Tx. The conventional ultrasonic wave transceiving device generates high frequency echo data and low frequency echo data based on echo signals of the sequential first and second ultrasonic signals FM(H)Tx and FM(L)Tx to obtain an echo image.
The conventional ultrasonic wave transceiving device transmits third ultrasonic signal CW(H)Tx and fourth ultrasonic signal CW(L)Tx sequentially in series. The third and fourth ultrasonic signals CW(H)Tx and CW(L)Tx have the same pulse length therebetween. The frequency of the signal forming the pulse of the third ultrasonic signal CW(H)Tx is higher than that of the fourth ultrasonic signal CW(L)Tx. The conventional ultrasonic wave transceiving device generates additional information based on echo signals of the sequential third and fourth ultrasonic signals CW(H)Tx and CW(L)Tx.
The conventional ultrasonic wave transceiving device repeats the transmissions of the first ultrasonic signal FM(H)Tx, the second ultrasonic signal FM(L)Tx, the third ultrasonic signal CW(H)Tx, and fourth ultrasonic signal CW(L)Tx as one group.
However, in the method of using the dual-frequency ultrasonic signals for the echo image generation and the additional information generation, respectively, a period of the transmissions of the two kinds of ultrasonic signals for the additional information generation and the receptions of the echo signals thereof intervenes between a period of the transmissions of the ultrasonic signals for a current echo image generation and the receptions of the echo signals thereof and a period of the transmissions of the ultrasonic signals for the next echo image generation and the receptions of the echo signals thereof. In this case, an interval between the transception periods for the echo image generation becomes longer by a transception period Tip for the additional information. Therefore, a transception cycle TEp for the echo image becomes longer, causing a delay in transmission cycle of the echo image.
Additionally, the period of the transmissions of the two kinds of ultrasonic signals for the echo image generation and the receptions of the echo signals thereof intervenes between a period of the transmissions of the ultrasonic signals for a current additional information generation and the receptions of the additional information thereof and a period of the transmissions of the ultrasonic signals for the next additional information generation and the receptions of the additional information thereof. In this case, an interval between the transception periods for the additional information generation becomes longer by the transception period for the echo image. Therefore, the generation interval of the additional information becomes longer, causing possible degradation in reliability.